Circulating gas lasers found in the prior art require a feed line and an outlet line for the laser gas to be exchanged. In a gas laser of that kind, the laser gas in the laser gas circuit is circulated by means of a circulation pump, e.g. a Roots pump, and the laser gas to be exchanged is sucked off through the outlet line by a further pump. In a typical CO.sub.2 high-performance laser, a pressure of 120 to 135 millibars is present on the high-pressure side of the laser gas circuit, i.e., between the Roots pump and the resonator. One problem that is encountered is that gas from the environment penetrates into the laser gas circuit due to leakage. This gas which leaks into the system impairs laser efficiency. For this reason, in the prior art, fresh gas is supplied to the laser gas circuit and a corresponding amount of laser gas is evacuated from the laser gas circuit. In this manner, the composition of the laser gas in the laser gas circuit is maintained on a purity level at which the laser output power is maximized.
The consumption of fresh gas is an essential cost factor in the operation of such gas lasers. Therefore, it is desirable that the fresh gas consumption be kept as low as possible. In the prior art, there have been attempts to purify the laser gas and remove undesired gas constituents by using an absorption means in the laser gas circuit. The use of an absorption means was intended to reduce the demand for fresh gas. The use of such an absorption means, however, produced undesirable side effects and altered the operation of the gas laser itself. In addition, the absorption means used in the prior art tends to become quickly saturated and regeneration of the absorber is difficult.